11 chem

Nucleotide

Monomer of nucleic acids made of phosphate, pentose sugar, nitrogenous base.

Nucleoside

Sugar + nitrogenous base (NO phosphate).

Nucleic Acid

Polymer of nucleotides linked by phosphodiester bonds.

Purines

Adenine (A) and Guanine (G); double-ring structure.

Pyrimidines

Cytosine (C), Thymine (T), Uracil (U); single-ring structure.

Ribose

Sugar in RNA; has OH on 2' carbon.

Deoxyribose

Sugar in DNA; has H on 2' carbon (no oxygen).

Condensation: Nucleoside Formation

Base + sugar → nucleoside + H2O.

Condensation: Nucleotide Formation

Nucleoside + phosphate → nucleotide + H2O.

Phosphodiester Bond

Link between 3' OH of one nucleotide and 5' phosphate of next.

DNA Structure

Double helix; antiparallel strands; complementary base pairing.

Antiparallel Orientation

One strand 5'→3', the other 3'→5'.

Complementary Base Pairs

A-T (2 H-bonds), G-C (3 H-bonds).

DNA Backbone

Alternating sugar and phosphate groups.

Base Pair Location

Interior of double helix.

RNA vs DNA

RNA: single-stranded, ribose, uracil; DNA: double-stranded, deoxyribose, thymine.

mRNA

Conveys genetic info from DNA to ribosome.

tRNA

Transfers amino acids to ribosome; has anticodon.

rRNA

Structural + catalytic part of ribosome.

Transcription

Process making mRNA from DNA template.

Translation

Process making protein using mRNA at ribosome.

DNA → mRNA Rule

A → U, T → A, C → G, G → C.

Template DNA Strand

Strand read 3' → 5' to synthesize mRNA 5' → 3'.

Coding DNA Strand

The DNA strand with same sequence as mRNA (except T vs U).

Genetic Code

Set of 3-base codons coding for amino acids.

Start Codon

AUG (methionine).

Stop Codons

UAA, UAG, UGA (terminate translation).

Translation of mRNA

Read codons 5' → 3' and convert to amino acid sequence.

Mutation

Change in nucleotide sequence of DNA.

Silent Mutation

Changes codon but NOT amino acid.

Missense Mutation

Changes amino acid in protein sequence.

Nonsense Mutation

Changes amino acid codon → stop codon.

Frameshift Mutation

Insertion/deletion not in multiples of 3; shifts reading frame.

Effect of mRNA Mutation

Can change protein sequence, shorten protein, or have no effect.

Point Mutation

Single base change.

Substitution

One base replaces another (may be silent/missense/nonsense).

Insertion

Adding nucleotide(s); often causes frameshift.

Deletion

Removing nucleotide(s); often causes frameshift.